The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 88, Issue 12

Scientific Articles | December 01, 2006

Patellofemoral Joint Kinematics in Individuals with and without Patellofemoral Pain Syndrome

N.J. MacIntyre, PT, PhD¹; N.A. Hill, MSc²; R.A. Fellows, MSc²; R.E. Ellis, PhD³; D.R. Wilson, DPhil⁴

¹ School of Rehabilitation Therapy, 31 George Street, LD Acton Building, Room 222, Queen's University, Kingston, ON K7L 3N6, Canada
² Department of Mechanical Engineering and Human Mobility Research Centre, Queen's University, Apps Wing, Doran 2, Kingston General Hospital, 76 Stuart Street, Kingston, ON K7L 2V7, Canada
³ Surgical Planning Laboratory, Department of Radiology, Room ASBI, L1-050, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115
⁴ Department of Orthopaedics, University of British Columbia and Vancouver Coastal Health Research Institute, 910 West 10th Avenue, Room 3114, Vancouver, BC V5Z 4E3, Canada

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In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from the Canadian Institutes of Health Research (CIHR MOP43883), the Natural Sciences and Engineering Research Council of Canada (Strategic Grant), the Ontario Centres of Excellence, the Ontario Research Fund, the Physiotherapy Foundation of Canada (AMMFOP), the Arthritis Society/Canadian Institutes of Health Research (research fellowship for N.J.MacI.), and the Canadian Arthritis Network (scholarship for D.R.W.). None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at the Human Mobility Research Centre, Queen's University and Kingston General Hospital, Kingston, Ontario, Canada

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2006 Dec 01;88(12):2596-2605. doi: 10.2106/JBJS.E.00674

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Abstract

Background: Patellofemoral pain syndrome is a prevalent condition in young people. While it is widely believed that abnormal patellar tracking plays a role in the development of patellofemoral pain syndrome, this link has not been established. The purpose of this cross-sectional case-control study was to test the hypothesis that patterns of patellar spin, tilt, and lateral translation make it possible to distinguish individuals with patellofemoral pain syndrome and clinical evidence of patellar malalignment from those with patellofemoral pain syndrome and no clinical evidence of malalignment and from individuals with no knee problems.

Methods: Three-dimensional patellofemoral joint kinematics in one knee of each of sixty volunteers (twenty in each group described above) were assessed with use of a new, validated magnetic resonance imaging-based method. Static low-resolution scans of the loaded knee were acquired at five different angles of knee flexion (ranging between —4° and 60°). High-resolution geometric models of the patella, femur, and tibia and associated coordinate axes were registered to the bone positions on the low-resolution scans to determine the patellar motion as a function of knee flexion angle. Hierarchical modeling was used to identify group differences in patterns of patellar spin, tilt, and lateral translation.

Results: No differences in the overall pattern of patellar motion were observed among groups (p > 0.08 for all global maximum likelihood ratio tests). Features of patellar spin and tilt patterns varied greatly between subjects across all three groups, and no significant group differences were detected. At 19° of knee flexion, the patellae in the group with patellofemoral pain and clinical evidence of malalignment were positioned an average of 2.25 mm more laterally than the patellae in the control group, and this difference was marginally significant (p = 0.049). Other features of the pattern of lateral translation did not differ, and large overlaps in values were observed across all groups.

Conclusions: It cannot be determined from our cross-sectional study whether the more lateral position of the patella in the group with clinical evidence of malalignment preceded or followed the onset of symptoms. It is clear from the data that an individual with patellofemoral pain syndrome cannot be distinguished from a control subject by examining patterns of spin, tilt, or lateral translation of the patella, even when clinical evidence of mechanical abnormality was observed.

Clinical Relevance: Since most patients with patellofemoral pain syndrome did not demonstrate abnormalities in patellar tracking during loaded knee flexion, other causative mechanisms must be explored to develop effective diagnostic and treatment strategies for this common musculoskeletal condition.

Figures in this Article

Patellofemoral joint pain is the most common problem involving the knee, affecting 25% of the general population^1-3. Many cases of anterior knee pain are diagnosed as patellofemoral pain syndrome, a largely idiopathic chronic pain disorder characterized by a gradual onset of poorly localized pain in the anterior aspect of the knee aggravated by activities such as squatting, stair climbing and descent, or prolonged sitting with the knee bent⁴. The diagnosis is based on the clinical history and the exclusion of other causes of anterior knee pain^1,5. In the general population, patellofemoral pain syndrome is most prevalent among adolescent and young adult women^6,7; however, this gender difference is not observed in highly physically active populations such as the military^7,8. Chronic patellofemoral joint pain is a serious problem since it limits mobility and may lead to arthritis and permanent disability. Despite the high prevalence of this disorder, its pathogenesis is not clearly understood.

Although it is widely held that patellar maltracking plays a role in the development of patellofemoral pain syndrome^5,9, this link has not been established. Patellofemoral pain syndrome has been attributed to abnormal patellofemoral joint mechanics caused by malalignment and tracking disorders, damage to the articular cartilage, and chronic overloading, although it has also been suggested that the syndrome is often not associated with a definable abnormality^5,10. Lower-limb biomechanical deficits that have been proposed to cause abnormal spin, tilt, and lateral translation of the patella can be identified in many cases of patellofemoral pain syndrome, but it is not clear that these are symptom-generating factors because similar types of malalignment have been observed in many people with no knee pain or disease^4,11,12. There may be no evidence linking specific kinematic parameters with the clinical symptoms in this disorder because no such link exists or because a sensitive and reliable noninvasive method of detecting differences in patellar kinematics has not been applied to study this question. Recently, in vivo methods have been developed to assess joint kinematics^13-19, but to our knowledge they have not been used to compare patterns of patellar tracking between patients with and those without patellofemoral pain syndrome.

In this study, we tested the hypothesis that patterns of patellar spin, tilt, and lateral translation can make it possible to discriminate individuals with patellofemoral pain syndrome and clinical evidence of patellar malalignment from those with patellofemoral pain syndrome and no clinical evidence of malalignment and from individuals with no knee problems.

Materials and Methods

Study Population

We studied members of the military community between the ages of eighteen and forty-five years. The study was approved by the research ethics board at our institution, and all volunteers provided written consent prior to participation. Exclusion criteria included any contraindications to magnetic resonance imaging, a history of any other injury or pathological condition involving the lower extremity, or positive signs of a meniscal, ligamentous, or iliotibial band lesion. One hundred and twenty potential subjects were assessed by the lead author to determine eligibility. Sixty volunteers were assigned to one of three groups on the basis of the history and the results of a battery of clinical tests (the McConnell patellar glide test, patellar apprehension test, patellar tracking [compression] test, passive patellar tilt test, Waldron squat test, flexion test, and palpation of the patellar facets). (See the Appendix for a description of each test and interpretation of the test results.) The first group comprised twenty subjects with patellofemoral pain syndrome and clinical signs of patellar malalignment (symptomatic group with malalignment), defined as a positive result on one or more of the first five tests listed above (Table I). The second group comprised twenty subjects with patellofemoral pain syndrome and no clinical evidence of patellar malalignment (symptomatic group without malalignment) (Table I). The etiology of the patellofemoral pain syndrome in this group was attributed to causes other than malalignment. Assignment to this group required negative results on the first four tests listed above and a positive result for pain on the Waldron squat test in the absence of catching or visible signs of malalignment of the patella, a positive result on the flexion test, or a positive result on palpation of the posterior medial or lateral margins of the patella. A control group of twenty volunteers with no history of knee trauma or clinical symptoms was recruited from the same military community. This group was selected to be comparable with the other groups with respect to age, gender, and physical activity level as determined by years of military service and level of involvement in sports activities.

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TABLE I Characteristics of the Study Population

Variable	Control Group	Symptomatic Group with Malalignment	Symptomatic Group without Malalignment
Gender	7 women, 13 men	7 women, 13 men	9 women, 11 men
Age*(yr)	30.4 ± 8.4	30.9 ± 9.2	36.0 ± 8.2
Height*(cm)	175.2 ± 10.0	176.9 ± 7.9	175.2 ± 10.8
Weight*(kg)	74.9 ± 16.5	77.9 ± 16.1	81.3 ± 16.1
Duration of military service*(yr)	9.0 ± 7.8, 6 civilians	11.6 ± 9.0, 3 civilians	13.7 ± 7.2, 6 civilians
Knee assessed	10 left, 10 right	10 left, 10 right	12 left, 8 right
Clinical test results†
History	0 positive	20 positive	20 positive
McConnell patellar glide test	0 positive	12 positive	0 positive
Apprehension test	0 positive	1 positive	0 positive
Patellar tracking (compression) test	0 positive	11 positive	5 positive
Passive patellar tilt test	0 positive	4 positive	0 positive
Waldron squat test	0 positive	9 positive‡	7 positive§
Flexion test	0 positive	6 positive	5 positive
Palpation of medial and lateral facets	0 positive	15 positive	13 positive

The values are given as the mean and standard deviation. †See Appendix for descriptions of clinical tests. ‡Positive for pain and crepitus, with lower-limb malalignment observed during squat. §Positive for pain and crepitus, with no lower-limb malalignment observed during squat.

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TABLE I Characteristics of the Study Population

Variable	Control Group	Symptomatic Group with Malalignment	Symptomatic Group without Malalignment
Gender	7 women, 13 men	7 women, 13 men	9 women, 11 men
Age*(yr)	30.4 ± 8.4	30.9 ± 9.2	36.0 ± 8.2
Height*(cm)	175.2 ± 10.0	176.9 ± 7.9	175.2 ± 10.8
Weight*(kg)	74.9 ± 16.5	77.9 ± 16.1	81.3 ± 16.1
Duration of military service*(yr)	9.0 ± 7.8, 6 civilians	11.6 ± 9.0, 3 civilians	13.7 ± 7.2, 6 civilians
Knee assessed	10 left, 10 right	10 left, 10 right	12 left, 8 right
Clinical test results†
History	0 positive	20 positive	20 positive
McConnell patellar glide test	0 positive	12 positive	0 positive
Apprehension test	0 positive	1 positive	0 positive
Patellar tracking (compression) test	0 positive	11 positive	5 positive
Passive patellar tilt test	0 positive	4 positive	0 positive
Waldron squat test	0 positive	9 positive‡	7 positive§
Flexion test	0 positive	6 positive	5 positive
Palpation of medial and lateral facets	0 positive	15 positive	13 positive

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Fig. 1:: The loading task. While lying supine on the magnetic resonance imaging-compatible knee loading rig, each subject loads his or her knee by pushing the heel against a foot plate connected to a magnetic resonance imaging-compatible spring. The surface of the foot plate is covered by textured anti-slip material, and the foot is secured to the plate with a loop-and-hook strap. The foot plate slides along the axis of the bore of the scanner and compresses the spring. All other translations and rotations are constrained. (Reproduced, with modification, from: Fellows RA, Hill NA, MacIntyre NJ, Harrison MM, Ellis RE, Wilson DR. Repeatability of a novel technique for in vivo measurement of three-dimensional patellar tracking using magnetic resonance imaging. J Magn Reson Imaging. 2005;22:145-53. Reprinted with permission.)

A physiotherapist blinded to group assignment measured the quadriceps angle (Q angle) in all of the study subjects with the exception of two in the group with patellofemoral pain syndrome and clinical signs of patellar malalignment, who did not attend for testing. A standardized testing procedure was used²⁰, and a positive result was recorded when the Q angle exceeded 15° for men and 20° for women²¹.

Procedure for Magnetic Resonance Imaging

Three-dimensional patellar tracking of each symptomatic and matched-control knee was assessed through a range of static loaded knee-flexion angles with use of a new, validated magnetic resonance imaging-based method^18,19. The method included four steps: (1) subject-specific bone models were generated from high-resolution magnetic resonance images, (2) coordinate systems based on anatomical landmarks were assigned to the bone models, (3) the models along with the coordinate axes system were registered (shape-matched) to osseous outlines obtained from a set of low-resolution images acquired while the subject lay supine on a custom magnetic resonance imaging-compatible rig and the knee was loaded at four, five, or six different angles of knee flexion, and (4) each component of patellar motion was determined as a function of knee flexion angle (see Appendix for details).

All images were acquired with a 1.5-T Signa Echo Speed Plus LX System (General Electric Medical Systems, Milwaukee, Wisconsin) with use of the whole-body coil. A high-resolution magnetic resonance imaging scan of each symptomatic knee and each matched-control knee was acquired with the knee positioned in relaxed extension. Each high-resolution scan was segmented to create subject-specific three-dimensional geometric models of the proximal part of the tibia, distal part of the femur, and patella with use of commercial software (Analyze 4.0 developed by Biomedical Imaging Resource [BIR], Mayo Clinic, Rochester, Minnesota, and distributed in North America by AnalyzeDirect, Lenexa, Kansas).

Subjects then performed a cycle of knee flexion in a custom magnetic resonance imaging-compatible loading rig¹⁸. The objective of the loading rig was to allow each subject to load one knee at various flexion angles in a closed-chain activity with a consistent force magnitude applied at the foot. Subjects loaded the imaged knee by pressing against a foot plate that was connected to an internal series of 0.625-in (1.6-cm) diameter cylindrical rubber stoppers that produced a magnetic resonance imaging-compatible (nonmetal) spring (Fig. 1). The angle of the foot plate was fixed. Compression of the spring was measured by a gauge that could be monitored from outside the bore of the magnetic resonance imaging scanner. The system was calibrated so that the spring compression required to resist an applied load of 152 N was known. Each participant was trained to apply load to the plate with the heel (rather than with the ball of the foot) to ensure that the direction of the applied force was predominantly along the axis of the scanner bore. Each subject's ability to reach and maintain the desired spring compression consistently using the knee extensors rather than the hip extensors was verified during training by ensuring contraction of the quadriceps muscle and smooth movement of the foot plate. An investigator present in the magnetic resonance imaging suite monitored compression of the spring and instructed the subject to adjust the applied force as required to maintain the spring compression at the target load of 152 N during image acquisition. Between each low-resolution scan (flexion angle), the magnetic resonance imaging bed was withdrawn from the bore of the scanner and the knee flexion angle was adjusted by repositioning the subject. The subject compressed the spring to the desired level, and foam pads were positioned under the knee to provide position feedback, but not support, to the back of the loaded knee.

Fast (approximately thirty-eight-second) low-resolution images were acquired of the knee in four, five, or six positions of static loaded flexion ranging between —4° and 60°. With use of Analyze 4.0 software, these low-resolution images were segmented and outlines of the tibia, femur, and patella were extracted. The relative positions of the geometric bone models at each position of loaded flexion were determined by registering (shape-matching) the bone models to the segmented bone outlines with use of the iterative closest points algorithm²². This algorithm depends on an accurate first guess of the model position; therefore, manual alignments of the models to data points were performed prior to registration.

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Fig. 2: The definitions of patellar motion for the three rotations (spin, tilt, and flexion) and the three translations (lateral, anterior, and proximal). The arrows indicate the direction of movement that has an increasingly positive value. M = medial, L = lateral, A = anterior, P = posterior, Pr = proximal, and D = distal.

Assigning Coordinate Systems

Orthogonal coordinate systems were assigned to each bone model, and the kinematic variables describing the orientation and position of the patella relative to the femur were represented according to the conventions of the joint coordinate system²³. The axes systems were assigned with use of anatomical landmarks as described in the literature for the proximal part of the tibia and distal part of the femur²⁴ and the patella²⁵. For right knees, positive directions were defined as proximal, lateral, and anterior, whereas for left knees, positive directions were defined as proximal, lateral, and posterior. For left knees, appropriate sign changes were made to convert the patellar rotations and translations to the right-knee conventions. The knee flexion angle was standardized across subjects by defining tibiofemoral joint flexion to be 7° in the high-resolution models since the positioning for this scan was consistent for all subjects.

Data Analysis

Kinematic measures of patellofemoral and tibiofemoral joint motion were calculated with use of an established gyroscopic convention²⁶. The orientation of the patella with respect to the femur was described by three rotations (Fig. 2): medial/lateral spin (rotation of the patella around the floating third axis such that medially directed motion of the superior pole of the patella results in positive values for spin), medial/lateral tilt (rotation about the patellar long axis such that posteriorly directed motion of the medial border of the patella results in positive values for tilt), and flexion/extension (rotation around the femoral flexion axis such that anteriorly directed motion of the superior pole of the patella results in positive values for flexion). The positions of the patella with respect to the femur (Fig. 2), described with use of components of a vector connecting the patellar and femoral origins, included medial/lateral translation (displacement along the component of the vector directed along the flexion axis of the femur such that lateral movement is positive), anterior/posterior translation (displacement along the component of the vector directed along the third axis of the femur such that anterior movement is positive), and proximal/distal translation (displacement along the component of the vector directed along the long axis of the femur such that proximal movement is positive). The patellar origin was fixed to the most posterior aspect of the bone-marrow interface at the midlevel of the patella²⁵. The origin of the coordinate system for the femur was fixed to the most distal point at the bone-marrow interface on the slice corresponding to the most superior level of the intercondylar notch²⁴. Flexion/extension of the tibia around the flexion axis of the femur was also calculated.

The null hypothesis that patellar spin, tilt, and lateral translation are not significantly different among patients with patellofemoral pain syndrome with clinical evidence of patellar malalignment, such patients without clinical evidence of patellar malalignment, and control subjects was tested with use of two-level hierarchical linear and nonlinear modeling (HLM 6 statistical package, ) with the data centered at 19° of knee flexion (see Appendix for details). The hierarchical linear and nonlinear modeling technique partitions the variance into that due to Level-1 (subject) and that due to Level-2 (group) variables. Alpha was preset at 0.05. For completeness, comparisons of group patterns of patellar flexion and anterior and proximal translations were also assessed.

Descriptive statistics were calculated with use of the Minitab statistical package (version 13; Minitab, State College, Pennsylvania). Group equivalence for subject characteristics was tested with use of a one-way analysis of variance. Alpha and beta were preset at 0.05 and 0.2, respectively.

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Fig. 3: The individual values, in degrees, for patellar spin (A and D), patellar tilt (B and E), and patellar flexion (C and F) plotted as a function of knee flexion angle (in degrees) for subjects in the control group (black circles), the group with patellofemoral pain syndrome and clinical signs of patellar malalignment (PFPS+mal) (red triangles in left column), and the group with patellofemoral pain syndrome without clinical signs of patellar malalignment (PFPS-mal) (red squares in right column). The solid lines represent the fit of the hierarchical linear modeling for the group with patellofemoral pain syndrome and clinical signs of patellar malalignment (red lines in left column), the group with patellofemoral pain syndrome without clinical signs of patellar malalignment (red lines in right column), and the control group (black lines).

Results

Study Population

There were no significant differences among the groups with respect to gender, age, body habitus, or years of military service (Table I).

Patellar Kinematics

On an individual basis, there were large overlaps of the values for patellar kinematics measured in subjects with patellofemoral pain syndrome—with or without clinical evidence of patellar malalignment—and the control group (Figs. 3 and 4). The unconditional hierarchical linear modeling analysis demonstrated that a quadratic model provided the best fit to the patterns of patellar tilt and flexion as well as to the patterns of lateral, anterior, and proximal patellar translations. The best fit for the patellar spin data was a linear model. For the cohort tested, global maximum likelihood ratio tests showed that the addition of the independent variable (group) did not significantly improve the model fit to the data (p values ranged from 0.08 for patellar flexion to >0.50 for lateral translation). Nonetheless, post hoc tests demonstrated significant group differences in features of the model fit for patellar flexion, and lateral and anterior translations (Table II).

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Fig. 4: The individual values, in millimeters, for lateral patellar translation (A and D), anterior patellar translation (B and E), and proximal patellar translation (C and F) plotted as a function of knee flexion angle (in degrees) for subjects in the control group (black circles), the group with patellofemoral pain syndrome and clinical signs of patellar malalignment (PFPS+mal) (red triangles in left column), and the group with patellofemoral pain syndrome without clinical signs of patellar malalignment (PFPS-mal) (red squares in right column). The solid lines represent the fit of the two-level hierarchical linear modeling for the group with patellofemoral pain syndrome and clinical signs of patellar malalignment (red lines in left column), the group with patellofemoral pain syndrome without clinical signs of patellar malalignment (red lines in right column), and the control group (black lines).

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TABLE II Coefficients, 95% Confidence Intervals, and Reliability Estimates for Each Feature in the Patterns of Patellar Motion (Centered at 19° of Knee Flexion) for the Three Groups

	Estimation of Coefficient for Fixed Effect (95% Confidence Interval)
Patellar Motion	Control Group	Symptomatic Group with Malalignment	Symptomatic Group without Malalignment	Reliability Estimate
Spin
Y-intercept	0.663 (-1.002, 2.329)	0.178 (-2.184, 2.539)	-0.153 (-2.510, 2.204)	0.913
Instantaneous slope	0.059 (0.011, 0.107)	0.021 (-0.048, 0.091)	-0.067 (-0.134, 0.001)	0.511
Tilt
Y-intercept	11.708 (8.757, 14.660)	-0.132 (-4.306, 4.041)	0.009 (-4.164, 4.181)	0.975
Instantaneous slope	0.143 (0.058, 0.229)	-0.095 (-0.219, 0.028)	-0.104 (-0.226, 0.017)	0.846
Rate of change in slope	-0.006 (-0.009, -0.002)	-0.005, (-0.010, 0.000)	-0.003 (-0.008, 0.002)	0.597
Flexion
Y-intercept	-0.564 (-2.865, 1.738)	-0.372 (-3.626, 2.883)	0.082 (-3.170, 3.334)	0.954
Instantaneous slope	0.601 (0.540, 0.663)	-0.039 (-0.129, 0.052)	0.036 (-0.051, 0.124)	0.709
Rate of change in slope	-0.001 (-0.005, 0.003)	0.005 (-0.000, 0.010)	0.006 (0.001, 0.012)	0.593
Lateral translation
Y-intercept	-1.477 (-3.064, 0.109)	2.250 (0.007, 4.493)	0.557 (-1.687, 2.800)	0.967
Instantaneous slope	-0.085 (-0.137, -0.034)	0.021 (-0.054, 0.095)	0.011 (-0.062, 0.084)	0.841
Rate of change in slope	0.003 (0.002, 0.005)	-0.001 (-0.003, 0.001)	-0.001 (-0.003, 0.001)	0.150
Anterior translation
Y-intercept	27.585 (26.318, 28.853)	-0.212 (-2.004, 1.580)	-0.745 (-2.537, 1.046)	0.979
Instantaneous slope	0.013 (-0.023, 0.048)	0.006 (-0.045, 0.057)	0.012 (-0.039, 0.063)	0.864
Rate of change in slope	-0.006 (-0.008, -0.005)	0.003 (0.001, 0.005)	0.001 (-0.001, 0.003)	0.584
Proximal translation
Y-intercept	20.789 (18.407, 23.172)	1.083 (-2.286, 4.452)	-1.039 (-4.408, 2.330)	0.968
Instantaneous slope	-0.704 (-0.760, -0.647)	0.010 (-0.072, 0.093)	-0.038 (-0.118, 0.042)	0.739
Rate of change in slope	0.004 (0.002, 0.006)	0.001 (0.000, 0.003)	0.001 (-0.001, 0.004)	0.323

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TABLE II Coefficients, 95% Confidence Intervals, and Reliability Estimates for Each Feature in the Patterns of Patellar Motion (Centered at 19° of Knee Flexion) for the Three Groups

	Estimation of Coefficient for Fixed Effect (95% Confidence Interval)
Patellar Motion	Control Group	Symptomatic Group with Malalignment	Symptomatic Group without Malalignment	Reliability Estimate
Spin
Y-intercept	0.663 (-1.002, 2.329)	0.178 (-2.184, 2.539)	-0.153 (-2.510, 2.204)	0.913
Instantaneous slope	0.059 (0.011, 0.107)	0.021 (-0.048, 0.091)	-0.067 (-0.134, 0.001)	0.511
Tilt
Y-intercept	11.708 (8.757, 14.660)	-0.132 (-4.306, 4.041)	0.009 (-4.164, 4.181)	0.975
Instantaneous slope	0.143 (0.058, 0.229)	-0.095 (-0.219, 0.028)	-0.104 (-0.226, 0.017)	0.846
Rate of change in slope	-0.006 (-0.009, -0.002)	-0.005, (-0.010, 0.000)	-0.003 (-0.008, 0.002)	0.597
Flexion
Y-intercept	-0.564 (-2.865, 1.738)	-0.372 (-3.626, 2.883)	0.082 (-3.170, 3.334)	0.954
Instantaneous slope	0.601 (0.540, 0.663)	-0.039 (-0.129, 0.052)	0.036 (-0.051, 0.124)	0.709
Rate of change in slope	-0.001 (-0.005, 0.003)	0.005 (-0.000, 0.010)	0.006 (0.001, 0.012)	0.593
Lateral translation
Y-intercept	-1.477 (-3.064, 0.109)	2.250 (0.007, 4.493)	0.557 (-1.687, 2.800)	0.967
Instantaneous slope	-0.085 (-0.137, -0.034)	0.021 (-0.054, 0.095)	0.011 (-0.062, 0.084)	0.841
Rate of change in slope	0.003 (0.002, 0.005)	-0.001 (-0.003, 0.001)	-0.001 (-0.003, 0.001)	0.150
Anterior translation
Y-intercept	27.585 (26.318, 28.853)	-0.212 (-2.004, 1.580)	-0.745 (-2.537, 1.046)	0.979
Instantaneous slope	0.013 (-0.023, 0.048)	0.006 (-0.045, 0.057)	0.012 (-0.039, 0.063)	0.864
Rate of change in slope	-0.006 (-0.008, -0.005)	0.003 (0.001, 0.005)	0.001 (-0.001, 0.003)	0.584
Proximal translation
Y-intercept	20.789 (18.407, 23.172)	1.083 (-2.286, 4.452)	-1.039 (-4.408, 2.330)	0.968
Instantaneous slope	-0.704 (-0.760, -0.647)	0.010 (-0.072, 0.093)	-0.038 (-0.118, 0.042)	0.739
Rate of change in slope	0.004 (0.002, 0.006)	0.001 (0.000, 0.003)	0.001 (-0.001, 0.004)	0.323

Patellar Rotations

Large variability was observed in the patterns of patellar spin and tilt across all three groups (Fig. 3, A, B, D, and E) and no significant group differences were detected. On the average, the patella rotated slightly medially as the knee was flexed in the group with patellofemoral pain syndrome and clinical signs of patellar malalignment and in the control group (Fig. 3, A), whereas little patellar rotation was observed in the group with patellofemoral pain syndrome and no clinical signs of patellar malalignment (Fig. 3, D). In all groups, the patella tilted medially over the initial 20° to 30° of knee flexion (Fig. 3, B and E). In the control group, the patella then tilted laterally approximately the same amount over the remainder of the knee flexion range. In both symptomatic groups, the average rate and magnitude of lateral tilt observed after the patella entered the trochlear groove appeared to be greater than that observed in the control group, but these differences were not significant and this portion of the pattern was influenced by relatively few data points as reflected in the reliability estimate (Table II).

In all groups, the patella flexed approximately 38° with knee flexion (Fig. 3, C and F). In the symptomatic group without malalignment, the rate at which patellar flexion increased after entering the trochlear groove was greater than that in the control group (p < 0.05). However, the reliability estimate for the rate of change in flexion was 0.59 compared with a reliability estimate of 0.95 for the magnitude of patellar flexion at 19° of knee flexion (Table II).

Patellar Translations

Through the range of knee flexion assessed, the patella shifted medially during the initial 30° to 35° of knee flexion before shifting laterally by approximately the same amount (Fig. 4, A and D). In the symptomatic group with malalignment, the patella was positioned more laterally through the full range of knee movement tested. At 19° of knee flexion, this difference was 2.25 ± 1.12 mm (mean and standard error) (p = 0.049; Fig. 4, A).

In all groups, the patella shifted slightly anteriorly until just after it entered the trochlear groove and then translated posteriorly as the knee flexed further (Fig. 4, B and E). However, the rate of posterior shift in the symptomatic group with malalignment was slightly less than the rate of posterior shift in the control group (p = 0.01). The reliability estimate for the rate of change in posterior translation was 0.58 as compared with a reliability estimate of 0.98 for the magnitude of patellar posterior translation at 19° of knee flexion (Table II). As expected for all groups, the patella shifted distally as the knee flexed (Fig. 4, C and F).

Discussion

The objective of our study was to determine whether patterns of patellar spin, tilt, and lateral translation make it possible to discriminate individuals with patellofemoral pain syndrome and clinical evidence of patellar malalignment from those with patellofemoral pain syndrome and no clinical evidence of malalignment and from individuals with no knee problems. In the cohort tested, the only significant difference in kinematics was a more lateral shift of the patella at 19° of flexion in the group with patellofemoral pain syndrome and clinical evidence of malalignment. The most clinically relevant findings were the large overlaps among individual values for all patellar motions. This suggests that many cases of patellofemoral pain syndrome are not associated with malalignment.

Consistency between our measurements of patellar tracking in control subjects and values reported in the literature^13-17 supports our approach. Our finding of a patellar shift of about 4 mm from a lateral to a medial position through the initial 32° of knee flexion, which reversed to a lateral shift through the remainder of the range of knee flexion, was also reported in two recent in vivo kinematics studies^14,17. We observed this general pattern of a lateral-to-medial shift in all three groups, which confirms that this pattern is not a pathological finding in individuals with patellofemoral pain syndrome and clinical evidence of patellar malalignment. Our finding of medial patellar tilt (approximately 7°) through the first 33° of knee flexion followed by lateral tilt (approximately 5°) through the remainder of the range is comparable with findings from most ex vivo studies¹³. Initial medial tilt, when observed in vivo, occurred during the first 30° of knee flexion and ranged in magnitude from 3.7° to 4.5°^13,17. Thus, we believe that the finding of increased angulation between the lateral facet of the patella and the lateral articular surface of the trochlear groove in the early range of knee flexion observed in all three of our groups is not indicative of pathology.

It is difficult to compare the pattern of patellar spin that we observed with that in previous studies because there was wide variation within our control group and variable patterns have been reported in the literature¹³. Our finding that the patella gradually rotated medially (approximately 3.7°) as the knee was flexed is consistent with a recent observation of "valgus" rotation (2° on the average) at 30° of knee flexion that increased in magnitude through the remaining 30° of knee flexion assessed¹⁷. Our findings are in agreement with those of others who observed no difference in two-dimensional radiographic values for patellar lateral tilt, patellar lateral shift, patellar angle, sulcus angle, and patellar height measured at 35° of knee flexion²⁷. These findings were interpreted to be consistent with those of previous investigators²⁸ who reported that if any abnormalities in patellar alignment exist in subjects with patellofemoral pain syndrome they are minimized once the patella enters the trochlear groove.

Most of our kinematic findings are consistent with the accepted understanding of the etiology of patellofemoral pain syndrome. Our finding that at 19° of knee flexion the patella was positioned more laterally in the symptomatic group with malalignment than in the control group is consistent with the fact that the majority of individuals (twelve) in the former group had a positive result of the McConnell patellar glide test (i.e., symptoms on resisted knee extension were decreased when a medial glide of the patella was passively maintained). One possible explanation for this observed pattern is weakness of the vastus medialis head of the quadriceps muscle. We did not assess the function of the vastus medialis muscle in our cross-sectional study, and the relationships among in vivo muscle function, patellar maltracking, and clinical symptoms remain unclear. It is not surprising that we observed no significant difference in patellar spin between the symptomatic groups and the controls given the high variability in patterns of spin among all subjects across the range of knee flexion assessed in our study. This variability is consistent with previous reports of variable patellar spin (rotation)¹³. Anatomical variation in the insertion of the vastus lateralis into the patella has been shown to result in different directions of patellar spin through an initial small range of knee flexion²⁹, which may explain the variable patterns of patellar spin observed within each subject group in our study. Differences in the rate of patellar flexion and the rate of posterior translation between individuals with patellofemoral pain syndrome and control subjects can be explained by changes in muscle action and tibiofemoral kinematics. The faster rate of patellar flexion with knee flexion in the symptomatic group without malalignment may have been due to altered patterns of quadriceps muscle activation that fail to counteract the rate of flexion as the patella tracks in the trochlear groove. Differences in tibiofemoral motion may also explain some of our observations. While internal and external tibial rotation have no effect on patellar flexion³⁰, faster posterior patellar translation and faster flexion could be caused by a tibia that translates posteriorly more rapidly with flexion.

This study had some limitations. First, most of the clinical tests used to assess alignment of the patella and determine group assignment are quite subjective. The clinical tests have limited reliability^20,31, and little research has been completed to determine their diagnostic accuracy³². Our findings with regard to quadriceps angles (Q angles) are consistent with those in previous reports showing that many patients with patellofemoral pain syndrome have a Q angle within the normal range³³. Moreover, we found that the subjects in our study who had an excessive Q angle when standing with the quadriceps relaxed were not the same eight subjects with the most laterally positioned patellae during loaded knee flexion. These results suggest that including the Q-angle test in the battery of tests used to assign volunteers to subgroups would not have changed the results of the study. A second limitation of our study was that we did not simulate the full range, flexion rate, and load of weight-bearing movement. There may be differences in patellar tracking between true continuous flexion and the range of static loading positions that were used in our study. A third limitation is that there is no accepted, meaningful approach for calculating the power of a study to reject the null hypothesis when hierarchical linear modeling is used. It is recommended that ten subjects per independent variable be recruited³⁴. Therefore, twenty subjects per group is expected to be sufficient to ensure confidence that we had sufficient statistical power to detect differences in patterns of patellar motion between the groups with patellofemoral pain syndrome and the controls. Finally, we did not perform a radiographic assessment of participants' patellar alignment, which is part of standard care in some practice environments. However, we believe that the clinical pathway used in this study, in which conservative treatment for patellofemoral pain syndrome was based on clinical tests in the absence of radiographs, is widely used.

Our results have implications for the understanding of the etiology of patellofemoral pain syndrome, its detection, and its treatment. First, our finding of few detectable differences in kinematics does not support the use of patellar tracking or alignment as an indicator of normal or abnormal joint function. It is important to note, however, that just because we detected few differences in kinematics does not suggest that there are no differences in force distribution or contact area at the joint. Second, the variation in individual data in all groups suggests that it probably is not possible to define a general standard of normal and abnormal kinematics for the purpose of guiding treatment. It would be desirable to find diagnostic tools that accurately subclassify patients with patellofemoral pain syndrome in order to identify those who will respond favorably to treatments that target kinematic changes. However, in the cohort tested, individuals with patellofemoral pain syndrome had patterns of patellar tracking that overlapped substantially with normal values and the clinical tests used to assess patellar malalignment did not reflect the patellar motion observed during loaded knee flexion. Third, this large variation suggests that investigators examining the relationship between biomechanics and clinical symptoms to study interventions should focus on paired designs connecting biomechanical changes caused by single treatments with pain relief. Our results suggest that other putative causes of patellofemoral pain syndrome (e.g., overuse⁵ or neurogenic factors³⁵) should be explored and objective clinical diagnostic tests must be developed in order to accurately identify patients with patellofemoral pain syndrome who will respond preferentially to intervention strategies targeting the specific causative factor(s).

Appendix

Details related to the magnetic resonance imaging procedure and the statistical methodology (hierarchical linear modeling) are available with the electronic versions of this article, on our web site at (go to the article citation and click on "Supplementary Material") and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM). ?

Acknowledgements

Note: The authors acknowledge Randy Booth, BScPT, M Manip Ther, and Dr. Crawford, MD, at the Medical Unit, Royal Military College and Canadian Forces Base, Kingston, for assistance with recruitment; Sarah Pardy, MScPT, and Lorelie Ade, BScPT, for the assessment of Q angles; Sue McKendry and Cyndi Little-Harper, Imaging Services, Kingston General Hospital, for technical assistance with magnetic resonance image acquisition; and Andrew Day, MSc, Senior Biostatistician in the Kingston General Hospital Clinical Research Unit, for assistance with the statistical analysis.

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Cutbill JW, Ladly KO, Bray RC, Thorne P, Verhoef M. Anterior knee pain: a review. Clin J Sport Med. 1997;7: 40-5.740 1997 [PubMed][CrossRef]

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Fairbank JC, Pynsent PB, van Poortvliet JA, Phillips H. Mechanical factors in the incidence of knee pain in adolescents and young adults. J Bone Joint Surg Br. 1984;66: 685-93.66685 1984 [PubMed]

Katchburian MV, Bull AM, Shih YF, Heatley FW, Amis AA. Measurement of patellar tracking: assessment and analysis of the literature. Clin Orthop Relat Res. 2003;412: 241-59.412241 2003 [PubMed][CrossRef]

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Patel VV, Hall K, Ries M, Lindsey C, Ozhinsky E, Lu Y, Majumdar S. Magnetic resonance imaging of patellofemoral kinematics with weight-bearing. J Bone Joint Surg Am. 2003;85: 2419-24.852419 2003 [PubMed]

Fellows RA, Hill NA, MacIntyre NJ, Harrison MM, Ellis RE, Wilson DR. Repeat-ability of a novel technique for in vivo measurement of three-dimensional patellar tracking using magnetic resonance imaging. J Magn Reson Imaging. 2005;22: 145-53.22145 2005 [PubMed][CrossRef]

Fellows RA, Hill NA, Gill HS, MacIntyre NJ, Harrison MM, Ellis RE, Wilson DR. Magnetic resonance imaging for in vivo assessment of three-dimensional patellar tracking. J Biomech. 2005;38: 1643-52.381643 2005 [PubMed][CrossRef]

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Topics

knee joint ; patella ; vibration ; patellofemoral pain syndrome ; patellofemoral joint ; patellofemur malalignment ; kinematics ; knee flexion ; patellofemoral lateral tracking

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Norma J. MacIntyre, PT, Ph.D.

Posted on January 10, 2007

Dr. MacIntyre and Dr. Wilson respond to Dr. Grelsamer

School of Rehabilitation Science, McMaster University, Hamilton, ON CANADA

We thank Dr. Grelsamer for his interest in our study(1) and for this opportunity to clarify our work.

While we agree with Dr. Grelsamerâ€™s concern that the term â€˜patellofemoral syndromeâ€™ is problematic, the term remains widely used and, more importantly, is generally well defined by researchers who use it. A search of the term â€˜patellofemoral pain syndromeâ€™ in MEDLINE, CINHAL, and AMED databases yielded 40 articles published in 2006. Among these were 4 Cochrane Reviews of the numerous primary articles describing specific treatments for â€˜patellofemoral pain syndromeâ€™(2-5). It appears that the authors using this term recognize the limitations inherent in its use and address this by clearly defining the characteristics of their patient populations as we have done in our paper(1).

We would like to emphasize that we identified participants with patellofemoral joint pain who, under current best clinical practice, would be referred for conservative treatment. We aimed to identify the subgroup of patients for whom treatment would focus on improving patellar tracking by using a battery of clinical tests to assess patellar alignment and dynamic patellar motion. Currently when other specific causes of patellofemoral joint pain cannot be identified, the assumption underlying treatment is that altered mechanics plays a causative role in many cases (even though evidence for this is not extensive). In the subgroup with patellofemoral pain and clinically observed malalignment (PFPS+mal), the MRI-based measures of patellar motion revealed that the patella was positioned slightly more laterally as the patella enters the trochlear groove. However, on an individual level, large overlaps in values were observed in comparison with the subjects in the other two groups. We conclude that â€œOur findings do not support the use of patellar tracking or alignment as an indicator of normal or abnormal joint function.â€ We donâ€™t see a major inconsistency in stating that the pathogenesis of patellofemoral pain syndrome is not clearly understood and that our results are consistent with current understanding because our findings add to the evidence that patellar maltracking is not a clinically significant factor for most individuals with patellofemoral joint pain.

The results of the clinical tests performed in our screening assessment would direct the focus of that treatment. Specifically, patients who tested positive for iliotibial band tightness or on the Hughstonâ€™s plica test were excluded. We chose to exclude these conditions since the extensor mechanism and patellofemoral joint pain would not be the primary focus of treatment. Conservative treatment for patients who test positively on the McConnell patellar glide test would involve taping, bracing or exercises based on the principle that positioning the patella more medially reduces pain. Similarly, observed malalignment of the lower limb or â€˜catchingâ€™ of the patella on the squat test would direct treatment towards improving the lower limb biomechanics during functional activities. Therefore, participants with positive results for these tests were assigned to the PFPS+mal group. We wish to correct the description of our use of the patellar tracking (compression) test that is given in our manuscript. As summarized in Table 1 in our paper, 11 symptomatic patients with clinical evidence of malalignment and 5 symptomatic patients with no clinical evidence of malalignment tested positively(1). This test result was only used to assign recruits to either one of the symptomatic groups or to the control group. We agree that a positive test result only confirms patellofemoral joint pain and does not provide information regarding alignment of the patella.

Our results do not support Dr. Grelsamerâ€™s interpretation that only 5 subjects in our PFPS+mal group were â€œlikely to exhibit malalignment on physical examination.â€ We did not specifically explore the relationships between clinical test results and associated kinematic measures because this was not the primary objective of the study and, as such, it was not appropriately powered to address this objective. A re-examination of our data shows that the individual values for lateral translation for the 5 patients Dr. Grelsamer identified as â€œlikely to exhibit malalignmentâ€ (Figure 1, red symbols) are not obviously different from the values for the other 15 subjects included in this group (Figure 1, black symbols). It is clear that the results for these individuals are very close to the mean values for the entire PFPS+mal group and have not skewed the observations for lateral translation. Data from recruits testing positive on other clinical tests used to detect problems with patellar alignment and dynamic motion also contributed to the finding that the patella is positioned slightly more laterally in this symptomatic group. This additional analysis supports our position that Dr. Grelsamerâ€™s concern that only 25% of our PFPS+mal group had clinical malalignment is unfounded. We believe that the group definitions used in our study are clinically relevant and our results provide important evidence to guide decision making in the conservative treatment of patients with patellofemoral joint pain.

Fig. 1. Individual values for lateral patellar translation as a function of loaded knee flexion angle in the PFPS+mal Group. Red circles: 4 subjects with positive patellar tilt test. Red triangles: 1 subject with positive apprehension test.

References:

1. MacIntyre NJ, Hill NA, Fellows RA, Ellis RE, Wilson DR. Patellofemoral joint kinematics in individuals with and without patellofemoral pain syndrome. J Bone Joint Surg Am 2006;88:2596-2605.

2. Heintjes E, Berger MY, Bierma-Zeinstra SMA, Bernsen RMD, Verhaar JAN, Koes BW. Pharmacotherapy for patellofemoral pain syndrome. The Cochrane Library. 2006;4:CD003470.

3. Heintjes E, Berger MY, Bierma-Zeinstra SMA, Bernsen RMD, Verhaar JAN, Koes BW. Exercise therapy for patellofemoral pain syndrome. The Cochrane Library. 2006;4:CD003472.

4. Dâ€™hondt NE, Struijs PAA, Kerkhoffs GMM, Verheul C, Lysens R, Aufdemkampe G, Van Dijk CN. Orthotic devices for treating patellofemoral pain syndrome. The Cochrane Library. 2006;4:CD002267.

5. Brosseau L, Casimiro L, Robinson V, Milne S, Shea B, Judd M, Wells G, Tugwell P. Therapeutic ultrasound for treating patellofemoral pain syndrome. The Cochrane Library. 2006;4:CD003375.

Ronald P Grelsamer, M.D.

Posted on December 19, 2006

There Is No "Patellofemoral Pain" Syndrome

Mount Sinai Medical School, New York, NY

To The Editor:

I have two major concerns regarding the recent article by MacIntyre, et al.(1). The first is that the authors discuss kinematics in patients with â€œpatellofemoral syndromeâ€, a syndrome that has never existed even though the term has been commonly used. Banishment of this term is one of the very few things that all members of the International Patellofemoral Study Group have agreed upon from the inception of this group in 1995(2,3). A medical syndrome is associated with a well-defined set of signs, symptoms, laboratory values, imaging studies and so forth. There is no such set of parameters associated with the â€œpatellofemoral syndromeâ€. Patients who might at one time have been diagnosed with patellofemoral syndrome are now recognized to, in fact, suffer from a wide variety of completely unrelated conditions. A diagnosis by exclusion (i.e. â€œI do not understand why you have painâ€) does not constitute a syndrome. Yet this seems to be the authorsâ€™ main criterion when they state that â€œThe diagnosis is based on the clinical history [what history specifically denotes a patellofemoral syndrome?] and the exclusion of other causes of anterior knee pain.â€

Are saphenous nerve neuromas, tight iliotibial bands, core deficiencies and plicas part of the patellofemoral syndrome or are they in the â€œother causesâ€? If they are part of the â€œother causesâ€ why are the various forms of malalignment singled out as being part of the patellofemoral syndrome and not also part of the â€œother causesâ€? If, on the other hand, they are all included under the umbrella of the â€œpatellofemoral syndromeâ€, how can we expect any common thread among them other than pain? Thus, it is not clear to me how the authors can state that â€œMost of our kinematic findings are consistent with the accepted understanding of the etiology of patellofemoral pain syndromeâ€ when they also state that the patellofemoral syndrome is â€œpoorly understoodâ€.

My second major concern is that the authors allegedly looked at 20 military recruits with patella malalignment and compared them to 40 recruits without malalignment. On further inspection, however, only 5 patients were likely to exhibit malalignment on the physical examination--4 patients with a positive patellar tilt test and the one patient with a positive apprehension sign. The others had a positive glide test (relief of pain with medial displacement), compression test (pain with compression of the patella) and/or squat test (pain when performing a squat). These tests reflect irritation under and around the patella with or without chondral lesions, but none is an automatic reflection of malalignment.

In the end, the authors examined 60 military recruits with anterior knee pain, 5 of whom demonstrated malalignment on physical examination. The fact that patients with and without malalignment exhibited similar kinematics can be easily explained by the fact that the authors added 15 subjects without malalignment to their â€œmalalignmentâ€ pool.

The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated.

References:

1. MacIntyre, NJ, et al., Patellofemoral Joint Kinematics In Individuals with and without Patellofemoral Pain Syndrome. Journal Bone and Joint Surg Am 2006;88:2596-2605

2. The International Patellofemoral Study Group, Grelsamer RP,: Patellofemoral semantics: the tower of Babel. 1997;Am J Knee Surg. 10 (2):92.

3. Grelsamer RP: Patellar Nomenclature â€“ The Tower of Babel Revisited. Symposium on patellofemoral arthroplasty. 2005;Clin Orthop 436:60-65.

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N.J. MacIntyre, N.A. Hill, R.A. Fellows, R.E. Ellis, D.R. Wilson; Patellofemoral Joint Kinematics in Individuals with and without Patellofemoral Pain Syndrome. The Journal of Bone & Joint Surgery. 2006 Dec;88(12):2596-2605.

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